feat(ms22-p2): add Discord channel → agent routing

- Add DISCORD_AGENT_CHANNELS env var for channel-to-agent mapping
- Route messages in agent channels to specific agents via ChatProxyService
- Handle SSE streaming responses and Discord's 2000 char limit
- Add workspace owner lookup for chat proxy authentication
- Add comprehensive unit tests for agent channel routing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/bridge/matrix/matrix-bridge.integration.spec.ts

@@ -28,6 +28,7 @@ import { StitcherService } from "../../stitcher/stitcher.service";
 import { HeraldService } from "../../herald/herald.service";
 import { PrismaService } from "../../prisma/prisma.service";
 import { BullMqService } from "../../bullmq/bullmq.service";
+import { ChatProxyService } from "../../chat-proxy/chat-proxy.service";
 import type { IChatProvider } from "../interfaces";
 import { JOB_CREATED, JOB_STARTED } from "../../job-events/event-types";
 
@@ -192,6 +193,7 @@ function setDiscordEnv(): void {
 
 function setEncryptionKey(): void {
   process.env.ENCRYPTION_KEY = "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef";
+  process.env.MOSAIC_SECRET_KEY = "test-mosaic-secret-key-minimum-32-characters-long";
 }
 
 /**
@@ -205,6 +207,10 @@ async function compileBridgeModule(): Promise<TestingModule> {
     .useValue({})
     .overrideProvider(BullMqService)
     .useValue({})
+    .overrideProvider(ChatProxyService)
+    .useValue({
+      proxyChat: vi.fn().mockResolvedValue(new Response()),
+    })
     .compile();
 }